LENSINK R, BIJTEL HJV VAN DER & SCHOLS RM (1989) Invasion of Redpolls Carduelisflammea in the Netherlands in 1986. LIMOSA 62 (1): 1-10.

Unidentified Redpoll Carduelis cabaret/flammea In autumn 1986, an invasion of Redpolls was recorded in the Netherlands. On 39 observation points 372 counts of visible migration were conducted (fig. I) lasting from half an hour before to two hours after sunrise (333 mornings). Counts at Eemshaven (112), Driebergen (303), and Kijkduin (419) lasted nearly the whole day (112 days). The first Redpolls were seen in the beginning of November, the last birds at the end of December (fig. 2). Three waves were recorded, of which only the first one entirely reached the west coast. Peak numbers differed from some tens per hour in the lowlands, through 200 in the eastern half of the country, to 900 per hour along the west coast (fig. 3). The second and third waves only partly reached the western half of the country (fig. 4). Fewer birds passed the western and northern lowlands. Hardly any Redpolls were seen on the Dutch Frisian Islands and in the northwest (fig. 3). The median date of migration shifted from west to east (fig. 4), with prolonged migration in the east. and no migration after week 48 in the west. It is calculated that at least 5.5 million Redpolls must have passed through the Netherlands. The average flight direction of Redpolls was SW (fig. 5, 6). In the beginning of November the flight direction shifted more to the south, but returned to SW later on (fig. 5). Going over the country from NW to SE the proportion S-E-N increased (fig. 6). Some leading line migration occurred (fig. I, 6). Most birds probably did not cross the SW part of the country, and are suggested to have headed at that point SE and S (fig. 6). Already before sunrise Redpoll migration started (fig. 7); migration at night was recorded several times. Along the coast migration took only place during the first half of the day, in the eastern half it lasted the entire day (fig. 8). This marked difference is probably induced by night and early morning migration over open areas, places which Redpolls do not like to cross during the day. The Redpolls migrated on average in large flocks. The average flock size per day was correlated with the logarithm of the total per day. Hence, the largest flocks occurred during the peak of migration (fig. 9). During the day the largest flocks occurred in the afternoon (fig. 10). The origin of the invasion was located in northern Fenno-Scandinavia and the northern Sovjet Union (fig. I I). The Alps, southern France, or Great Britain were not reached, so it is concluded that it ended in the Benelux and returned through Central Europe. The movement was recorded in southern Finland at the end of September. The peak in Latvia and Poland was reached in in the middle of October, at the beginning of November in Denmark and mid-November in the Netherlands. These figures suggest a migration speed of about 40-50 km a day.

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